Conventional bicycle frames are assemblies built from individual tubes which are secured together by welding, brazing or by using other means for joining the tubes. In naming the structural members of bicycle frames, the individual frame tubes were designated by their location in relation to the other major components or assemblies used to make up the functioning bicycle. Thus, it was that the short frame tube which supported the "head" axle joining the handlebar assembly and the front wheel fork was referred to as the "head" tube, the tube which supported the seat post and was connected to the pedal axle support (the bottom bracket) was referred to as the "seat" tube, the tube which joined the head tube and the top of the seat tube was referred to as the "top" tube, the tube which descended from the head tube to the bottom bracket was referred to as the "down" tube, the pair of tubes which descended from the seat tube to the ends of the rear wheel axle, with one tube on either side of the rear wheel, were referred to as the "seat stays", and the pair of tubes which connected the bottom bracket to the ends of the seat stays at the rear wheel axle, with one tube on either side of the rear wheel, were referred to as the "chain stays".
The multiplicity of connections required to secure these individual structural parts together, combined with the different forces encountered by the bicycle as it is ridden, cause a variety of problems. It is not unusual, for example, for one or more of the joints or connections on a conventional bicycle frame to fail, making the entire frame unsuitable for use until the connection is repaired. For many frames, the cost of straightening the frame and repairing the connection is prohibitive.
Further, the individual tubes and associated joints are relatively heavy since the tubes are generally made by the extrusion of or by the rolling and seaming of a metal alloy, and the joints are generally made by welding or brazing these tubes together. The manufacture and assembly of these multiple structural parts is also time consuming and costly.
In addition, most conventional bicycle frame tubes have generally circular cross-sections, since they are made from standard, commercial tubing. Thus, due both to the shape of the tubes and to the multiplicity of connection joints, conventional frames are not particularly adaptable to improved aerodynamics.
Prior efforts have been made to address some of these problems. For example, U.S. Pat. No. 4,513,986 to James Trimble suggests a monocoque type frame having a stressed, unitary outer skin over internal stiffening ribs and other structural elements. U.S. Pat. No. 3,833,242 to Thompson, Jr. discloses a frame having a hard exterior skin covering a structural foam interior. The Thompson frame was constructed by techniques disclosed in U.S. Pat. Nos. 3,268,636 and 3,456,446 to Angell, Jr. A partial listing of other molded frames and/or construction methods includes U.S. Pat. Nos. 3,233,916; 3,375,024; 3,884,521; and 4,015,854; and U.K. Patent No. 1,361,394.
These frames may provide advantages over conventional bicycle frames, due in some instances to increased strength and a reduced number of major structural joints. However, these frames generally require interconnection of a large number of interior structural support elements such as shear webs, reinforcing angles, reinforcing blocks and strips, and joining blocks, and/or the presence of structural foam in the interior to support the frame, thus sharing certain deficiencies with conventional frames. In addition, the construction methods employed therein are labor intensive and do not appear readily adaptable to efficient mass production.
The above problems may be remedied by a generally hollow bicycle frame made from resin and fiber composite materials as described hereinbelow. This frame may be constructed from lightweight, strong and relatively inexpensive composite materials, and there also is described a method for producing such a bicycle frame.